There isn't really any comparison.
The Delta is probably the best of its style of line, yet still based on tapers of the era they were designed in. A different design philosophy compared to today.
The WA 55 is a shooting head with a heavily weighted arse end vs. the delta. And no rear taper at all. 15' rio 8 wt sink tips are easily cast on the WA. The line is designed with 8wt tips to about 120 grains in mind.
Tips will be about the same for either line. I think the stock delta tips are slightly heavier...but can't remember. Since you are planning on using a 15' rod you will have more leeway than a short stick in this department.
Flip a coin. Delta lines are super smooth but IMO harder to cast. WA 55's are quite similar to the 45's, just a little longer with a few more grains while still packing a nice wallop. Its that wallop that gets you out of trouble when casting under less than ideal situations. That wallop also gets you in trouble if you overpower the rod regardless of the situation.